With the recent developments in communication technology, users have come to obtain required information by using various communication devices to access a predetermined server, regardless of the location of the users and the time of day. Users can confirm required information anytime by using, for example, cellular phones, PDAs (Personal Digital Assistants), etc.
For the administrator of the server, it may be required to restrict free access to the server. In this case, for example, it is common that the IP addresses of devices which are allowed to access the server are registered beforehand, and users accessing the server are requested to input passwords.
By way of example, when predetermined information is delivered only to persons gathering for an event, access is restricted by registering beforehand the addresses of devices used by those persons.
However, in order to restrict access, in the case of registering beforehand the IP addresses of all the devices for which the server allows access, a problem occurs in that the operation is very complicated.
Although such a problem does not occur when the number of the devices allowed to access is relatively small, when the number is as large as several hundred or several thousand, the operation of registering the IP addresses of all the devices becomes very difficult.
In addition, as described above, when access is restricted by requesting users to input passwords notified to them beforehand, there is a possibility that some users may forget their passwords. Also, even if the users remember the passwords, they are inconvenienced by having to input their passwords, which is a problem.